The overall objectives of this ongoing research program are to define, in as exact molecular and cellular terms as possible: 1. How the immunological system of man, and particularly of the growing organism from fetal life through adolescence, normally contributes to the maintenance of health, 2. The ways in which pathological processes affecting the immunological system produce clinical disease, 3. How these disease processes may be affectively combatted. This involves a combined clinical, chemical, morphological, and genetic approach to the control of antibody and complement synthesis through a study of the complement defects and the primary immunodeficiency syndromes, their pathogenic consequences, and their therapy. At the cellular level, B and T lymphocyte function in man is under investigation from the point of view of defects or aberrations in these cell lines.